Improve the implementation of get_perspective

[miselico]

In Deck, the method get_perspective fullfills two functions

1. providing the overall perspective
2. providing the perspectives of the players

What is returned is decided based on both the signature of the Deck and the specified player. I would change this to two methods, one for each of the functionalities above.
The signature would then only be used as an access control mechanism.

Even without this, the current functionality could be written less concise, but more clear as

	if self.__signature == 1:
		assert player == 1 or player == None, "You are not allowed to access the game of player 1 trough this state"
		return list(self.__p1_perspective)
	elif self.__signature == 2:
		assert player == 2 or player == None,  "You are not allowed to access the game of player 2 trough this state"
		return list(self.__p2_perspective)
	elif self.__signature == None:
		if player is None:
			return self.__card_state
		else:
			if player == 1: return list(self.__p1_perspective)
			else: return list(self.__p2_perspective)
	else:
		raise Exception("Deck.__signature invalid!")